Beefy Boxes and Bandwidth Generously Provided by pair Networks
The stupid question is the question not asked
 
PerlMonks  

Re^10: Moose and default values

by tobyink (Abbot)
on Feb 20, 2013 at 23:54 UTC ( #1019865=note: print w/ replies, xml ) Need Help??


in reply to Re^9: Moose and default values
in thread Moose and default values

In this case what I'd suggest is a custom type constraint.

use Moose::Util::TypeConstraints; subtype 'TrueStr', as 'Str', where { !!$_ }; coerce 'TrueStr', from 'Any', via { $_ || "whatever" }; has foo => (is => "ro", isa => "TrueStr", coerce => 1);

Then any value which is not a TrueStr will be coerced into one via the code $_ || "whatever".

Of course, this also applies to accessors, not just the constructor. (Not a problem for a read-only attribute though!) And also, it means that if you've got a bunch of attributes like this, each with different defaults, you need to define a type constraint for each one.

The alternative - attribute metaprogramming - starts off seeming simple enough, but becomes more complicated when you start thinking about immutability. (Attribute metaprogramming can be a real bitch when it touches on immutability.)

A compromise would be to hook has to automatically build per-attribute type constraints and coecions. I submitted a patch to MooseX::AttributeShortcuts for precisely this feature some months ago, but it was only partly accepted: per-attribute constraints are now supported, but not coercions.

package Cow { use Moo; has name => (is => 'lazy', default => sub { 'Mooington' }) } say Cow->new->name


Comment on Re^10: Moose and default values
Select or Download Code

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1019865]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others lurking in the Monastery: (14)
As of 2014-07-28 21:30 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    My favorite superfluous repetitious redundant duplicative phrase is:









    Results (209 votes), past polls